This invention relates to new and improved ternary alloys, to aqueous electrolytic baths from which the alloys are deposited, and to a process for forming the alloys.
Various alloys have been developed in efforts to duplicate the superior color of chromium and alloys containing substantial amounts of chromium, while also providing the corrosion resistance and tarnish resistance required when the alloy is to be used as a protective coating. Accordingly, the prior art teaches the addition of brightening agents to plating baths for the electro-deposition of tin-nickel binary alloys, as in U.S. Pat. No. 3,141,836 --Seyb et al, or the careful control of plating conditions, also in the deposition of nickel-tin binary alloys, such as the highly acidic baths in U.S. Pat. No. 2,926,124-- Taylor et al. In another approach cobalt-tin binary alloys have been studied with respect to close similarities in corrosion resistance to nickel-tin alloys. Clarke et al, "An Electrodeposited Bright Tin-Cobalt Intermetallic Compound, CoSn," Transactions of the Institute of Metal Finishing, 1972, Volume 50.
Despite the usefulness of such alloys from the standpoint of tarnish and corrosion resistance, those of such alloys which initially exhibited brightness similar to that of chromium did not maintain the good color. Moreover, results in obtaining hardness, brightness, tarnish resistance and color stability have not been consistent. Such properties tend to be overly sensitive to specific process conditions and therefore are difficult to reproduce on a commercial scale.